In conventional, top-emitting optoelectronic devices, such as vertical-cavity surface-emitting lasers (VCSELs), the semiconductor substrate serves not only as the base for fabrication of the emitters, but also as the mechanical supporting carrier of the emitter devices after fabrication. The terms “top” and “front” are used synonymously in the present description and in the claims in the conventional sense in which these terms are used in the art, to refer to the side of the semiconductor substrate on which the VCSELs are formed (typically by epitaxial layer growth and etching). The terms “bottom” and “back” refer to the opposite side of the semiconductor substrate. These terms are arbitrary, since once fabricated, the VCSELs will emit light in any desired orientation.
An attempt to create bottom-emitting VCSEL devices was reported by Roscher, in “Flip-Chip Integration of 2-D 850 nm Backside Emitting Vertical Cavity Laser Diode Arrays” (Annual Report 2002, Optoelectronics Department, University of Ulm). According to this report, arrays of substrate-side emitting VCSELs were directly hybridized onto silicon fanouts by means of an indium solder bump flip-chip technology, using electrical contacts formed on the top side of the VCSEL wafer.